Various proposals have been made to reduce the weight of vehicle bumpers while increasing their energy absorbing characteristics so as to eliminate or reduce damage during low impact collisions.
One approach has been to mount compressible energy absorbing plastic material on a rigid bumper beam. In order to provide secondary energy absorption in such systems it has been proposed that a collapsible plate like member be embedded in the compressible energy absorbing plastic material as shown in U.S. Pat. No. 3,856,613. While suitable for their intended purpose, such systems add weight to the vehicle and require special tooling to form the compressible energy absorbing plastic material around the components which form the collapsible plate like member.
Another approach, shown in U.S. Pat. No. 3,656,791, provides a vehicle bumper with a fascia covering an inflatable air bag. The air bag is located behind the fascia during normal use. On impact the air bag breaks through the fascia destroying it and exposing the air bag to damage as it extends beyond the fascia to be directly exposed to an impacting object. Under such modes of operation there is a high likelihood of rupture of the air bag on impact. Such rupture releases the inflatant in an uncontrolled manner such that the device no longer provides impact absorption under controlled conditions. Additionally, during normal operation there is no provision for releasing the inflatant material from the air bag to provide a controlled rate of energy absorption which will avoid damage to the bumper system.
Other prior art bumpers with an air bag component located in a position to be easily ruptured are shown in U.S. Pat. Nos. 3,971,583 and 4,176,858 wherein a hollow impact cushion 20 receives the impact force and is exposed to possible tearing or rupture. The air from the cushion 20 is forced into a rigid cylinder air tight section 20 of the bumper. The air tight section 20 is difficult to manufacture and maintain.
U.S. Pat. No. 3,695,665 discloses a shock absorbing bumper in which a hollow tubular bumper member is located. The hollow member is filled with a fluid which will be released into a hollow expandable member when the vehicle is impacted so as to absorb energy. The provision of fillable secondary containers increases the weight of the bumper system and requires elaborate piping in association with the primary bumper components.
Other approaches to provide energy absorption in vehicle bumpers are set-forth in U.S. Pat. Nos. 3,689,054; 3,822,076; 3,922,002; 3,960,397; 4,061,385; 4,215,878; and 4,706,990. None of the energy absorption systems disclosed in these patents are as pertinent as those above-discussed. Further, they do not disclose or suggest an energy absorbing system having a fascia backed by a compressible energy absorbing plastic and also an air bag operative to provide energy absorption in addition to that of the compressible energy absorbing plastic material. Nor do these patents suggest an arrangement in which a compressible energy absorbing plastic material is configured to enclose and shield an inflatable air bag system or gas bladder which is operative on vehicle impact to provide energy absorption in addition to that of the compressible energy absorbing plastic material so as to avoid damage to the vehicle under low impact conditions up to vehicle speed of 10 miles per hour.